Internal Dataflow Error

Sebastian Dröge sebastian at
Tue Feb 4 15:25:04 CET 2014

On Di, 2014-02-04 at 15:15 +0600, aft wrote:

> > alawdec is a decoder element, and it needs to know what the input caps
> > are in order to interpret and process the data properly. filesrc will
> > not set any caps whatsoever on the buffers, it will just read them and
> > push them downstream.
> >
> > If alaw was a typefindable format, you could just add a 'typefind'
> > element between filesrc and alwadec, but it's not typefindable.
> >
> What is this "type findable format"? Which of the "elements" are type
> findable and why?

alaw is not type-findable because there are no magic bytes or any known
headers or really anything in there that distinguishes alaw from random

All of the container formats (MP4, AVI, WAV, MKV, Ogg, ...) are
type-findable, and some codecs like h264 too.

For those GStreamer can guess the caps after reading some bytes of

> > From the filename I would guess that the file is in fact a WAV file,
> > which means you need to use a 'wavparse' element before the decoder, so
> > try e.g.:
> >
> >  filesrc location=foo.wav ! wavparse ! alawdec ! audioconvert !
> > autoaudiosink
> Is the wav demuxer mandatory? I mean if put "caps" appropriate for
> cpm-alaw explicitly would that work? Or i need a demuxer every time i
> try to read a "container" media format?

wav demuxer is not mandatory, but any container format and the
corresponding demuxer element will make your life much easier.

Without you will have to a) set the caps and b) make sure that buffers
are provided in appropriate sized chunks to the decoder.

Sebastian Dröge, Centricular Ltd -
Expertise, Straight from the Source
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